Shift device for a transmission and power divider of a motor vehicle having such a shift device

ABSTRACT

A shift device for a transmission, which comprises a sliding sleeve, a shift fork engaging in the sliding sleeve, and an actuator that can rotate on a shaft that is disposed at an angle to the transmission shaft. In order to provide a simple and reliable control that satisfies all functional requirements, a cam having two flanks and a flattened section on the maximum radius is disposed on the shaft. On the base of the shift fork, two interacting pushrods are disposed at a fixed distance so that one pushrod rests against the one flank and the other pushrod rests against the other flank and one pushrod rests against the flattened section in at least one extreme position.

BACKGROUND OF THE INVENTION

The invention relates to a shift device for a transmission, consistingof a shift sleeve, displaceable in the direction of the axis of atransmission shaft, for the driving connection of transmission members,of a shift fork engaging into the shift sleeve, and of, as actuator, anelement which is rotatable on a shift shaft arranged transversely to thetransmission shaft and which cooperates with a foot part of the shiftfork.

It is known from WO 01/59331-A to adopt, as actuator a pinion whichmeshes with a corresponding toothing on the foot part of the shift fork,the shift shaft being driven by an electric gear motor.

This has some disadvantages: the step-up of this movement transmissionis constant, which, as a rule, does not correspond to the profiledesired for shifting and to the characteristic of the electric motor;especially not when the shift sleeve has synchronization. There are nostops, and the toothing has no blocking action, that is to say it cannotretain the shift sleeve in the respective position. Both factors,however, are particularly important in the case of an electromotivedrive. The motor is, of course, to remain currentless after a completedchangeover and is even to be capable of being uncoupled in specificapplications, even when changeover took place counter to the ever-actingforce of a spring. Furthermore, to simplify the control, the motor is tobe capable of being moved up against a stop, in order to manage withoutposition or speed sensors.

In order to remedy this, the object of WO 01/59331-A is to provide adetent disk firmly connected to the rotating element and a detent memberengaging into a detent recess. Said detent member holds the rotatingelement after the uncoupling of the electric motor and ensures that thisis possible only after a defined end position is reached. However, thisremedy is highly complicated and is also not entirely satisfactory infunctional terms. Due to the moments acting on the element andconsequently on the detent disk (which emanate, for example, from thesynchronization or from chamfers of the teeth in order to secure thesleeve against a stop), friction arises which obstructs or completelyprevents the changeover. This may also occur when the two elements to becoupled are in an unfavorable relative position. The other gear in eachcase then cannot be engaged, and the sleeve remains set in the neutralposition, which may lead to hazardous driving situations and thereforeshould not happen. Moreover, due to the long tolerance chain,positioning is inaccurate.

The object of the invention, therefore, is to propose a simple andreliable control which satisfies all functional requirements, inparticular safety requirements.

SUMMARY OF THE INVENTION

The foregoing object is according to the invention, by means of thefollowing:

a) the rotatable element is a cam which has two flanks extending from aminimum to a maximum radius and a flattening at the maximum radius,

b) two lantern wheels cooperating with the cam are provided at a fixeddistance from one another on the foot of the shift fork,

c) so that one lantern wheel bears against one flank and the otherlantern wheels bears against the other flank and, in at least one endposition, one lantern wheel bears against the flattening and the otherlantern wheel bears exactly against the minimum radius.

The cooperation of the cam of one member with the two lantern wheels ofthe other member, the two members having defined poles (one may beinfinitely remote), provides a desmodromic control. In this context, theflattening is formed. Thus, one lantern wheel, together with aflattening, brings about a detention of the shift fork in an endposition, and the other lantern wheel at the smallest radius gives riseto a stop. As a result, two functions, which it has been possible tofulfill only by means of two different pairs of members according to theprior art, are combined in a single pair of members, this being suchthat shifts can take place even counter to considerable holding forces.The lantern wheel pressing onto the flattening of the cam under theforce of the coupling spring does not, of course, exert any torque onthe cam. Furthermore, by the configuration of the cam shape, the step-upcan be adapted to the shift requirements (in contrast to a conventionallantern wheel toothing in which the step-up must of course be constant).

In a preferred embodiment, the shift fork is a two-armed lever pivotableabout an axis fixed with respect to the housing and the lantern wheelsare cylinders, the axes of which are parallel to the axis of the shiftshaft. This affords an accurate kinematic guidance of the two members,along with low friction; the latter to an especially great extent whenthe lantern wheels are rotatable about their axes. Furthermore, theflanks of the cam are enveloping curves of the lantern wheels when thereis a common rolling movement of cam and lantern wheels. In this case,the step-up ratio of the rolling movement can be determined by means ofthe configuration of one flank of the cam, that of the other flank thenarising from this.

In an advantageous development with a shift shaft driven by an electricmotor, a shoulder is provided at the point of minimum radius on at leastone flank. The electric motor can consequently be controlledautomatically without path or speed regulation.

In order to ensure reliable shifting, further measures mayadvantageously be taken: when the shift fork surrounds a shift sleevewith a large diameter, the foot part of the shift fork is appended atthe lowest point of the latter, the shift force thereby being introducedsymmetrically into the shift fork. When there is the risk that the shiftsleeve cannot be engaged in the case of a tooth-on-tooth position, theshift fork contains an elastic element, so that the foot part can moveback. When the tooth position is favorable, shifting then takes placesomewhat later by means of the force of the elastic element.

The invention is also concerned, particularly with regard to the powerdivider for motor vehicles, with an off-road gear step which can beshifted due to the axial displacement of one of its elements by means ofa shift fork as a result of rotation of a shift shaft arrangedtransversely to the axial direction. In the case of a power divider, theproblems referred to initially arise in a particularly disturbing way.They are eliminated by the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described and explained below with reference to figuresin which:

FIG. 1 illustrates a vertical section through a power divider having theshift device according to the invention,

FIG. 2 illustrates a section according to CC in FIG. 1,

FIG. 3 illustrates a detail of FIG. 2, enlarged and varied,

FIG. 4 illustrates a view according to IV in FIG. 3,

FIG. 5 illustrates the same as FIG. 4 in one end position,

FIG. 6 illustrates the same as FIG. 4 in the other end position,

FIG. 7 illustrates another embodiment in a view similar to that of FIG.4.

DETAILED DESCRIPTION

In FIG. 1, the housing of a power divider is designated as a whole by 1,an input shaft coming from the drive unit, not illustrated, of thevehicle by 2, a first output shaft drive-connected to the rear axle by 3and a second output shaft drive-connected to the front axle, likewisenot illustrated, by 4. The second output shaft 4, by means of a firsttoothed-belt wheel 5, drives, below the input shaft 2, a secondtoothed-belt wheel 6 which is seated on a driven shaft 7 for the driveof the front axle.

To distribute the torque to the two output shafts 3, 4, a differential,designated in summary by 10, is provided. Furthermore, a control unit 11below the differential 10 and a blocking clutch 12 for blocking thedifferential 10 are provided. In the exemplary embodiment shown, theblocking clutch is combined structurally with the differential 10. Itcould, however, also be arranged separately, indeed even anywhere elsein the power divider or in the drive train. The differential itself mayalso have a widely differing design within the framework of theinvention.

FIG. 1 and FIG. 2 show an exemplary and particular version of the powerdivider. Inside a differential housing 16, which serves here at the sametime as a planet carrier, are located a sun wheel 17 connected fixedlyin terms of rotation to the input shaft 2, planet wheels 18 of theoff-road gear step, which are mounted rotatably in the differentialhousing 16, and first compensating wheels 21 and second compensatingwheels 22. The former (21) are connected fixedly in terms of rotation tothe first output shaft 3 and the latter (22) are connected fixedly interms of rotation to the second output shaft 4. The differential housing16 is surrounded by a ring wheel 19 which is axially displaceable and,in the off-road gear, is connected fixedly in terms of rotation to thedifferential housing 16. This special embodiment of the differential 10is the subject of Austrian patent 405 157 and is described in moredetail there in terms of type of construction and functioning.

The blocking clutch 12 is actuated by means of two ramp rings 31, 32rotatable relative to one another. The first ring 31 possesses a firstramp lever 35, and the second ring 32 possesses a second ramp lever(36), said ramp levers projecting downward and possessing rollers 39 attheir free ends 37, 38. Between the two rollers 39 is located arotatable control disk 40. During the rotation of this control disk, therollers 39 are moved apart from one another and, via the ramp levers 35,36 moved in a scissor-like manner, the rings 31, 32 are rotated relativeto one another.

In FIG. 2, 47 is a motor output shaft of an electric gear motor, notillustrated, said motor output shaft rotating with a correspondingstep-down when the motor is running. Connected fixedly in terms ofrotation to this motor output shaft is a carrier shaft 48 which isslipped onto the latter in a sleeve-like manner and which is mounted onboth sides in the housing 1. The hub 49 of the control disk 40 and a cam50 are mounted rotatably on the carrier shaft 48. Between the hub 49 andthe cam 50, a changeover sleeve 52 is mounted fixedly in terms ofrotation, but displaceably in the longitudinal direction, on the carriershaft 48 by means of a longitudinal ball guide 51. The changeover sleeve52 is displaced by means of a changeover fork 53 which is actuated by achangeover magnet 54 (FIG. 1) via a lever mounted in a changeover forkaxis 55 (FIG. 1). The changeover sleeve 52, at its two axial ends, hasfirst shift teeth 56 for rotationally fixed connection to the hub 49 andsecond shift teeth 57 for rotationally fixed connection to the cam 50.The shift teeth 56, 57 are coupling teeth with a deflecting pressureangle. If only one gear shift or only one blocking clutch is to beactuated, a changeover sleeve 52 is not necessary.

It can be seen in more detail in FIG. 3 that the cam 50 cooperates in away still to be described with lantern wheels 60, 61 which are arrangedon the foot part 64 of a shift fork 63 which is pivotable about an axisof oscillation 62 in the housing and by means of which the ring wheel 19is displaced in the axial direction for changeover into the off-roadgear. For this purpose, a sliding block 66 is provided on each of thetwo sides of the ring wheel. An elastically flexible intermediate zone65 may be provided in the foot part 64.

In the exemplary embodiment shown, the cam 50 and the lantern wheels 60,61 are duplicated (cams 50* and lantern wheels 60*, 61*) for reasons oflateral guidance, and the foot part 64 of the shift fork 63 is tied tothe lowest point of the latter, hence in its axis of symmetry. By virtueof the latter aspect, the deformations of the two halves of the shiftfork 62 are equal, so that they cannot become jammed.

In FIG. 4, the kinematics of the cooperation of cam and lantern wheels60, 61 can be seen. The lantern wheels 60, 61 are arranged at a fixeddistance 70 from one another on the foot part 64 of the shift fork 63.Here, they are circular cylinders (other shapes may also be envisaged,see FIG. 7) with axes 71 which either are only geometric axes or areaxes of rotation for the lantern wheels, on which they can rotate andthus roll on the cam 50, in order to minimize friction. The cam isrotatable with its shaft about an axis 72 and possesses a first flank73, a second flank 74, at a maximum distance from the axis 72 aflattening 75, and at a minimum distance from the axis 72, that is tosay at a minimum radius, valleys 76, 77 which shoulders 78, 79 adjoin.The flanks 73, 74 are shaped in such a way that in all the middlepositions, such as, for example, in FIG. 4, the lantern wheel 60 alwaysbears against the flank 73 and the lantern wheel 61 always bears againstthe flank 74. These flanks are therefore enveloping curves of the twolantern wheels. In contrast to a toothing, by means of a suitableshaping of the flanks 73, 74, different step-ups can be implemented as afunction of angle. It can also be seen directly in FIG. 4 how, forexample, a rotation of the cam 50 clockwise about its axis 72 causes apivoting of the shift fork 63 counterclockwise about its axis ofoscillation 62.

In FIG. 5, the cam 50′ is in one end position. The lantern wheel 61′ hasrun through the valley 77′ and reached the stop 79′. As a result, theelectric motor driving the cam has been stopped and reversed, so that,when switched on again, it rotates in the opposite direction. In thisposition, the other lantern wheel 60′ is supported on the flattening75′. Since the supporting force, illustrated by an arrow 80, is directedtoward the axis 72′ of the cam 50′, no torque is in this case exerted onthe cam 50′. The shift fork can thus be held in the position shownwithout action upon the motor and without locking. If appropriate, forsafety purposes, a spring, not illustrated, is provided or a couplingspring, present in any case, acts as such. The other end position ofFIG. 6 differs from that of FIG. 5 only in that the lantern wheels 60″,61″ have exchanged their rollers, and in that the cam 50″ is rotatedclockwise approximately through a right angle. The shift fork isretained, here, in the other end position.

The possibility of providing an elastic zone 65 in the foot part 64 ofthe shift fork 63 was mentioned further above. When the ring wheelcannot be engaged in the case of a tooth-on-tooth position, the elasticzone allows the cam 50 to execute its adjusting movement as far as theend position, but without the fork itself being moved in this case. Onlywhen the teeth of the ring wheel have been displaced somewhat withrespect to its counterwheel is the ring wheel engaged by means of theforce stored in the elastic zone.

In the variant of FIG. 7, the cam 150 is to a very great extent widenedand thickened. It cooperates kinematically with the lantern wheels 160,161 which are not cylindrical here, but bar-shaped, and are providedwith suitably shaped sliding surfaces 178, 179. Here, too, between thetwo members a desmodromic movement transmission prevails, in which thetwo contact surfaces 178, 179 are always in contact with the cam 150.

1. A shift device for a transmission comprising: a shift sleevedisplaceable in a first direction for the driving connection oftransmission members; a shift fork for engaging said shift sleeve; anactuator including: a rotatable element rotatably supported on a shaftand arranged transversely to said first direction, said rotatableelement cooperating with a foot part formed on said shift fork; a camdefined by a flattening and a pair of flanks extending therefrom, saidcam rotatable about a cam axis; and a pair of lantern wheels cooperatingwith said cam at a fixed distance from one another on said foot partsuch that a first lantern wheel bears against a first flank and a secondlantern wheel bears against a second flank; wherein at least one of saidfirst and second lantern wheels bears against said flattening when saidcam is rotated to an end position.
 2. The shift device of claim 1,wherein said first and second flanks join said flattening at a maximumdistance from said cam axis and extend therefrom to a minimum distancefrom said cam axis.
 3. The shift device as recited in claim 1, whereinsaid shift fork comprises a two-armed lever pivotable about a first axisand said pair of lantern wheels are circular cylinders having axes whichare parallel to said first axis.
 4. The shift device as recited in claim3, wherein said pair of flanks envelope curves of said pair of lanternwheels during rotation of said cam and said lantern wheels.
 5. The shiftdevice as recited in claim 1, wherein said cam further defines ashoulder adjoining said first flank opposite said flattening and asecond shoulder adjoining said second flank opposite said flattening. 6.The shift device as recited in claim 1, wherein said foot part isconfigured at an end of said shift fork opposite said shift sleeve. 7.The shift device as recited in claim 6, further comprising an elasticelement supporting said foot part on said shift fork.
 8. The shiftdevice as recited in claim 1, further comprising a motor shaft coupledto said cam for driving rotation thereof.